linux-kernel - Re: [PATCH v4 05/11] media: cadence: csi2rx: Fix stream data configuration

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Date:   Thu, 7 Oct 2021 02:44:53 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Pratyush Yadav <p.yadav@...com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Nikhil Devshatwar <nikhil.nd@...com>,
        Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Benoit Parrot <bparrot@...com>,
        Maxime Ripard <mripard@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org
Subject: Re: [PATCH v4 05/11] media: cadence: csi2rx: Fix stream data
 configuration

Hi Pratyush,

Thank you for the patch.

On Wed, Sep 15, 2021 at 05:32:34PM +0530, Pratyush Yadav wrote:
> Firstly, there is no VC_EN bit present in the STREAM_DATA_CFG register.
> Bit 31 is part of the VL_SELECT field. Remove it completely.
> 
> Secondly, it makes little sense to enable ith virtual channel for ith
> stream. Sure, there might be a use-case that demands it. But there might
> also be a use case that demands all streams to use the 0th virtual
> channel. Prefer this case over the former because it is less arbitrary
> and also makes it very clear what the limitations of the current driver
> is instead of giving a false impression that multiple virtual channels
> are supported.

No issue with that. Hopefully we'll support multiple streams for real in
the not too distant future :-)

> Signed-off-by: Pratyush Yadav <p.yadav@...com>

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> ---
> 
> (no changes since v1)
> 
>  drivers/media/platform/cadence/cdns-csi2rx.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/platform/cadence/cdns-csi2rx.c b/drivers/media/platform/cadence/cdns-csi2rx.c
> index 3730e8beee48..edd56c5f2e89 100644
> --- a/drivers/media/platform/cadence/cdns-csi2rx.c
> +++ b/drivers/media/platform/cadence/cdns-csi2rx.c
> @@ -48,7 +48,6 @@
>  #define CSI2RX_STREAM_STATUS_RDY			BIT(31)
>  
>  #define CSI2RX_STREAM_DATA_CFG_REG(n)		(CSI2RX_STREAM_BASE(n) + 0x008)
> -#define CSI2RX_STREAM_DATA_CFG_EN_VC_SELECT		BIT(31)
>  #define CSI2RX_STREAM_DATA_CFG_VC_SELECT(n)		BIT((n) + 16)
>  
>  #define CSI2RX_STREAM_CFG_REG(n)		(CSI2RX_STREAM_BASE(n) + 0x00c)
> @@ -286,8 +285,11 @@ static int csi2rx_start(struct csi2rx_priv *csi2rx)
>  		writel(CSI2RX_STREAM_CFG_FIFO_MODE_LARGE_BUF,
>  		       csi2rx->base + CSI2RX_STREAM_CFG_REG(i));
>  
> -		writel(CSI2RX_STREAM_DATA_CFG_EN_VC_SELECT |
> -		       CSI2RX_STREAM_DATA_CFG_VC_SELECT(i),
> +		/*
> +		 * Enable one virtual channel. When multiple virtual channels
> +		 * are supported this will have to be changed.
> +		 */
> +		writel(CSI2RX_STREAM_DATA_CFG_VC_SELECT(0),
>  		       csi2rx->base + CSI2RX_STREAM_DATA_CFG_REG(i));
>  
>  		writel(CSI2RX_STREAM_CTRL_START,

-- 
Regards,

Laurent Pinchart